Joshua Garcia's pulse quickens every time he approaches a U.S. Border Patrol checkpoint. The staggered speed-limit signs on the side of the highway indicate that he should slow down from 40 to 30 to 20 miles per hour. Due to his experiences in the past, and unlike most other drivers, he follows the speed limits exactly.

Garcia has done nothing wrong. He is also a U.S. citizen. But he feels that sense of dread. It is like that feeling of trepidation pulling into, say, that checkpoint on the Colorado border where armed, uniformed officials could order you to pull over. Maybe this time, as on many occasions, they would just wave him through. Perhaps he'd be able to continue on his way back to Tucson as the harsh afternoon light softens into dusk. He hopes that is the case, because he has two kids from the youth council with him.

Sebastian, who is 17, is asleep in the back seat. Fifteen- year-old Amelia is pointing to a sign that says there are dogs on duty. "I want to pet the dog," she says. Garcia looks at Amelia and jokes, "They're working dogs, you're not supposed to pet them."

In addition to feeling nervous about approaching the checkpoint, there is also exhilaration and afterglow from a great day. That morning, when they drove from Tucson to the Tohono O'odham Nation, a beautiful and muscular wildcat walked across the two-lane road in front of them. "A mountain lion," the kids murmured. They had to look twice to make sure. And then they were sure. It was the first time either of them had seen one. It was the first time for Garcia, too, the adult leader who had spent thousands of hours walking in the desert. There is something about seeing an elusive and endangered animal, free and wild in its own habitat, that stays with you a long time. Conversations about the lion dominated for the rest of the day. Garcia believes that it was because of the lion that many in the group wanted to walk toward Baboquivari Peak, on a path that climbed to one of the caves where Itoi, the Tohono O'odham creator, resided. From the sacred cave there was a sweeping view of the O'odham aboriginal land that extended as far as the eye could see, including hundreds of miles into Mexico. For a moment there was no international border dividing the land, only the beauty one has of suddenly seeing a vast, inspiring landscape. At the cave they sang to the mountain. It was that sort of day, reconnecting with the living Earth with a sort of reverence that goes against the grain in much of the contemporary United States.

They can see the authorities wave another car forward. They can hear and smell the idling engines. It was another abnormally hot day during the year 2015, which would be the hottest year in recorded history up until that point (only to be surpassed by the very next year). Garcia puts his truck into gear and inches ahead. There are orange striped signs in the middle of the road. There is a stop sign with a trio of orange flags on top, slightly flapping around in the breeze. There are well-armed Homeland Security agents in forest-green uniforms observing his vehicle as he pulls forward into this modern-day bum blockade, located 45 miles north of the international border.

Of course, Garcia is not yet a climate refugee like the Dust Bowl migrants who were turned away from the California border in the 1930s, or the many people fleeing ecological, political, and economic disasters around the world today. A common misperception about border enforcement is that it targets only people on the other side. Lines like in a bum blockade, however, can be drawn quickly and anywhere at any time, including on all paved roads leaving the Tohono O'odham Native American reservation, creating essentially an extra layer of border security around a particular group of people. Our borders are constantly changing, and the same is true of whom and what they apply to, including U.S. citizens.

Borders may seem passive and static, but they are actually agressive and dynamic. As evidenced by the Trump administration's January 2017 executive order that banned travel from seven countries, CBP—after multiple days of blockading people from those countries into the United States—demonstrated that it has the will, capacity, and infrastructure to respond swiftly to commands.

Sophie Smith, an activist scholar based in Arivaca, Arizona, has studied the checkpoints that surround her small town and in the broader region. Smith says checkpoints start out as temporary, as did many of them in the Southwest in the post-9/11 era, then become part of border policing strategy. The checkpoints have become, Smith stressed, a "model that is workable in the rest of the United States."

Authorities, Smith says, "know how the checkpoints would function. They know and have the infrastructure. They know whom to contract; they have all the relationships with the public and private sector. The protocols already exist and are constantly evolving depending on the security situation."

According to former CBP commissioner Gil Kerlikowske, "the border is a nexus to a continuum of activities that threaten the national interests of both security and prosperity. In response, CBP will lead collaborative efforts that apply multidimensional pressure on those seeking to do us harm; outside U.S. borders, at the border, and into the interior regions of the country." What Kerlikowske is saying: it doesn't matter where you are; Border Patrol will be there too.

Indeed, as Garcia inches toward the three green-uniformed agents, he is in the 100-mile border jurisdiction area, a "zone of security," in Kerlikowske's words, that wraps around the contour of the United States. This zone was determined in the 1940s and 1950s when Border Patrol was a fraction of what it is today. The Immigration and Nationality Act stated that they can patrol a "reasonable distance" away from the border and the U.S. Supreme Court determined that reasonable distance was 100 miles. The expansion of the checkpoints happens like a heat wave. It happens gradually, then overtakes you. In fact, when I was doing the research for this book I could not pinpoint when exactly the Three Points checkpoint was installed. Nobody I asked knew. Was it 2006? 2007? The checkpoints appeared silently, with little fanfare. When asked, Homeland Security says that they are temporary, which in Arizona is technically true. According to the law, all checkpoints must be temporary. What "temporary" means is another issue, because the checkpoints that were installed around 2006 are, as of this writing, still there.

The Three Points checkpoint isn't exactly impressive—just a portable trailer with an attached tarp for shade—but it still qualifies, according to one of the Border Patrol's informational brochures, as "a critical enforcement tool for securing the nation's borders against all threats to our homeland." Authorities at the checkpoint stop every vehicle on the road, quickly look into each one, and then ask the people inside to verify their citizenship.

The surveillance dogs that Amelia wanted to pet sniff each car for traces of narcotics and explosives. According to the American Civil Liberties Union, this is one of the many ways that Homeland Security violates people's Fourth Amendment protection from search and seizure. According to the Border Patrol, such civil rights violations are worth it: "Our enforcement presence along these strategic routes reduces the ability of criminals and potential terrorists to easily travel away from the border."

When Garcia lurches ahead and finally reaches the authorties, they just wave him over to secondary inspection. Garcia looks at the nearest agent to say something, but the official just waves his hand, now slightly irritated, as if Garcia were a pesky fly. Secondary inspection means that an agent has detected something that requires closer examination. Perhaps it is the dog. Perhaps it is the officially sanctioned "wide discretion" an agent has to further invade your privacy. Perhaps it's your ethnicity, as Homeland Security is the only department officially permitted to use racial profiling as a pretext for detaining a person for questioning. When the Obama administration issued new rules in an attempt to curtail racial profiling, the one huge exception was DHS. As one DHS official told the New York Times, "We can't do our job without taking ethnicity into account. We are very dependent on that."

Garcia slowly drives into the secondary inspection site. He drives to where the armed agents are standing. He looks at Amelia and asks: "What happened to the phone that your mom gave you?" Amelia responds: "She took it back." Behind him, Sebastian is waking up, but his phone battery is dead.

Garcia does not, by his own admission, like conflict. He tries to avoid it. When he pulls into secondary he hears a forceful, a commanding voice yelling: "Get out of the vehicle!" The voice is urgent, as if there were explosives somewhere, as if there were a bomb, as if someone were in danger. The yelling has the urgency, the intensity of war. It is so urgent that Garcia briefly thinks that it must be something else. He finds it hard to believe that just a few minutes ago he was talking to Amelia about her dreams, about how she wanted to be a music teacher, about how she played in the orchestra, about how she wants to go to Japan. It was hard to believe that they were just talking softly about animals, remembering the mountain lion they had seen. The Homeland Security agent barks: "GET. OUT."

There is a term used on the Tohono O'odham reservation to describe the lingering side effects of a bad experience with Border Patrol: "checkpoint trauma." This is especially prevalent among little kids, says Amy Juan, a teacher and founding member of TOHRN (Tohono O'odham Hemajkam Rights Network). Kids could be playing, happy, smiling, laughing, but once they know they are in the vicinity of a checkpoint they shut down and become frightened. Although they are U.S. citizens, a massive enforcement apparatus encircles their traditional land and community, a modern-day "bum blockade."

RED DAWN

Now Garcia is thinking the worst. He remembers all the incidents that he's had with the Border Patrol since the upsurge in operations in the mid 1990s. He even remembers when this all began. Since he was young and growing up with his grandparents, he has always been very close to the land. He lived off the reservation, just west of Tucson, near Saguaro National Monument. Garcia loves to take long, slow walks in the desert. He knows the wildlife, the vegetation, and the saguaro fruit that his beloved grandmother taught him how to harvest. Garcia knows how to read the landscape, knows the subtle shifts of weather, when the nopal and the saguaro will flower and fruit. One spectacular October night in the 1990s, when he was a teenager, he saw bright flares light up the sky in a way he had never seen before. At first he was confused. Was there some sort of alien aircraft landing on the Tohono O'odham reservation? Then the sky filled up with helicopters and airplanes as if the flash opened a gate for the advent of homeland security.

"It was kind of like Red Dawn," he said referring to the movie that ridiculously depicts the invasion of the United States by North Korea. Garcia said that he knew something had, at that point, changed. This was confirmed a few days later, right after Halloween and the Day of the Dead, when there were trick-or-treater footprints coming and going all throughout his aunt's dirt lot. Border Patrol agents showed up, hyped up and in hot pursuit. At this point, there were more agents than ever before, though a fraction of what they are today.

When I first met Garcia, he would lay out very detailed stories about how the dynamics of climate change and aggressive law enforcement were impacting the Tohono O'odham Nation. In the same breath he would talk about the massive Homeland Security presence, the unreliability of the rains, and the subsequent out-of-sync fruiting of the saguaro or the prickly pear cactus. Perhaps there is no better place to witness the convergence of climate change and border militarization than on this reservation, a territory bisected by an unwanted international boundary more than a century ago. In the age of global warming, the reservation has become, according to veteran humanitarian activist Mike Wilson, a "prototype police state" for the rest of the country.

The report "Record of Abuse: Lawlessness and Impunity in Border Patrol's Interior Enforcement Operations," describes in detail the components of this model "police state." Agents' brandishing of weapons during normal traffic stops of Tohono O'odham members, the report says, has become routine. Border Patrol agents have stopped and detained a school bus "more than a dozen times;" each time they forced students to stand out in the heat as they rifle through their personal belongings. One family said that agents pulled them over after they returned home to retrieve a forgotten item, apparently, according to the agents, a "suspicious act." For the O'odham, the result is similar to living under occupation, a term used often in their communities.

Over the years, I have heard stories from many O'odham, most of whom wish to remain anonymous. I have heard about a Tohono O'odham health worker whom Border Patrol pulled over after she picked up patients to transport them to a dialysis center. I have heard about Border Patrol blocking a funeral procession and then showing up at the cemetery during the burial. I have heard about Border Patrol desecrating a burial ground—and other sacred places—by using it as a shooting range and by driving all over it with ATVs. A man told me that he was simply driving north from the international divide when Border Patrol pulled him over and six agents surrounded him, armed with high-caliber automatic weapons. They never informed him what it was that set them off. Tohono O'odham Nellie Jo David, a TOHRN member and student of indigenous peoples law and policy, put it this way: "We can't visit family, go to the store, attend meetings, participate in our culture, grab a bite somewhere, or say hi to our friends without being accused of something."

Using cases from heavily redacted documents obtained from Customs and Border Protection, the ACLU alleges that agents' "violent, reckless, and threatening" conduct is not that of just a few bad apples. The verbally and sometimes physically abusive routine conduct of the U.S. Border Patrol, according to the report, is not limited to the reservation. In one case, a Border Patrol agent told a woman to "put the fucking keys in the truck" at an interior checkpoint west of Tucson after a false canine alert. When she objected to the language, the agent responded by saying, "I can talk to you any fucking way I want." The agent then explained to his supervisor that he felt a "more forceful approach was needed in order to convey her need to follow my direction."

In another incident, a woman asked why the Border Patrol had detained her in Tucson, 60 miles north of the border, when she was driving in her car to drop off her two children at school in March 2011. The agents first told her that her Ford Expedition "was running low," and then: "We'll think of something."

The ACLU called these practices a "de facto stop and frisk" for border residents. It happens almost every single day, with very little attention or fanfare. The targeted mistreatment of indigenous communities is perhaps the most persistent form of racism in U.S. history, and harks back to white colonialism and Manifest Destiny. Such abuse offers a glimpse into what might one day become normal in the future of climate crisis and displacement. Worth stating again, the time is near when the very people who vehemently support a gigantic U.S. border wall may find themselves denied access to the other side.

Surveillance and racial profiling in the Southwest degrades millions of people from all walks of life. Former Arizona governor Raul Castro, for example, was detained and compelled to stand in 100-degree heat for more than 30 minutes while he was closely inspected. He was 96 years old at the time. Although the Border Patrol has made more than 6,000 arrests and confiscated 135,000 pounds of narcotics at checkpoints, records show that it was mostly U.S. citizens who were swept up, not criminals from other countries.

Surveillance and targeting of U.S. citizens is not new, and can only be expected to intensify under Donald J. Trump. For the 2018 U.S. federal budget, the Trump administration proposed to give a further jolt to already sky-high budgets for border and immigration enforcement. Trump plans to hire an additional 100 government lawyers and 1,500 new ICE and Border Patrol agents. An extra $2.6 billion will be designated to "high-priority tactical infrastructure and border security technology, including funding to plan, design, and construct a physical wall along the southern border." This is on top of existing budgets that already reach, it is worth remembering, about $20 billion annually (just counting CBP and ICE). A further $1.5 billion will go to expand incarceration, transportation, and expulsion of "illegal immigrants." Add to this an extra $54 billion extra going to the Pentagon, a 10 percent increase, and slashing the Environmental Protection Agency by 31 percent, further entrenching these preexisting dynamics, ensuring the occurrence of future climate catastrophes and the militarization to corral their aftermath. The advent of a new sort of Red Dawn is upon us—except the invader isn't North Korea, but the U.S. government occupying its own communities.

Although it is not explicitly stated, the maintenance and expansion of the checkpoint system is implied, which means the policing of U.S. citizens and potentially blockading their mobility—and activism in future scenarios, and in places far away from the southwest border.

In 2008, for example, a Border Patrol agent forced Vermont senior senator Patrick Leahy from his car at a checkpoint 125 miles south of the New York state border. The ACLU unearthed a prototype plan for Border Patrol to operate checkpoints on all five Vermont highways. On the Adirondack Highway, rumble pads slow down traffic headed south from Plattsburgh toward Albany. Rarely are the Homeland Security agents there, but the infrastructure is there for them to commence immediately. At a checkpoint near Watertown, New York, Border Patrol agents confiscated the car of a college student, pushed her to the ground, and electrocuted her with a stun gun.

In November 2016, the federal government deployed the U.S. Border Patrol at Standing Rock, North Dakota, where Native American groups accompanied by activists from across the country were trying to stop the construction of the Dakota Access Pipeline, which would carry oil from North Dakota to refineries and export terminals in the Gulf Coast and lock-in the equivalent of "30 coal plants" worth of emissions. According to the statement of the U.S. Border Patrol Grand Forks Sector, the federal Homeland Security agency started its operation there, much more than 100 miles from the international boundary, on November 20—though activists made claims that Border Patrol had been setting up roadside blockades well before then. The statement said the Border Patrol presence "was requested to assist with preserving life and protecting property in and around the Dakota Access Pipeline (DAPL) protest location."

One incident happened the morning of November 22, 2016, when a caravan of 200 cars set off on rural two-lane roads in North Dakota to do an action. About a half an hour in, police cars blistered past the caravan and set up a barrier, blockading the road. Two hundred cars had to suddenly brake to an abrupt halt, causing some rear-end collisions. People got out of the cars and engaged in a singing ceremony with plants in front of the police barricade. Ten green-striped U.S. Border Patrol vehicles pulled in. They told the people who were singing, according to student Nora Collins, who was present, "You are blocking off a public highway, you must leave now or we will begin arresting people." When people responded that it was the police who were blocking off the highway, the Border Patrol was "dismissive," according to Collins.

What Josh Garcia and the passengers in his car were about to experience has become increasingly normalized in the United States. "GET OUT," the agent bellows. Garcia, Amelia, and Sebastian get out of the car into the already oven-like heat of the afternoon. There is a constant smell of burning exhaust, pollution, and simmering asphalt. An agent enters the car and rifles through Sebastian's backpack. Does the 17-year-old who wants to be a visual artist have something that threatens national security?

Garcia does not know what to do. He wants to assert his rights, but he doesn't want to make a scene in front of the kids. Finally he says it: "We don't consent to a search." Garcia's voice is soft, calm, and barely audible to the agent, who continues treating Sebastian's backpack as if there were a bomb inside. Another green-uniformed agent approaches Garcia. He is walking in a straight line, right at him. He reaches for the club on his gun belt. He yells, "Get back!" Several men in gray uniforms with black hats and boots from the company G4S, the same private security firm where Omar Mateen worked before killing 49 people at Orlando's Pulse nightclub in 2016, stand up and walk briskly to join the Border Patrol agent. One of the G4S cops is eating an apple. He throws it to the ground, and joins the action.

G4S has a quarter-billion-dollar contract to provide securitized transportation for the undocumented people whom the Border Patrol arrest in the desert. The for-profit company has also identified extreme weather as a "potential source of business" to the Carbon Disclosure Project. G4S sees potential profits in droughts and famines, and quotes a United Nations projection of "50 million refugees" as if this assures that they will continue their lucrative border contract and maybe even get a few new ones. The privatized police force also deployed its agents during Hurricanes Katrina and Sandy and offered "security from social unrest." While underscoring their lessening carbon footprint, G4S also wrote, "Climate change presents a risk to people and infrastructure across the globe. As an organization that specializes in managing risk, we recognize that the threat of climate change is an important and growing concern for our group, our customers and communities."

In Three Points, the G4S agents are showing their ability to work checkpoints and intimidate young people. "We don't consent," Garcia says, backpedaling, along with the kids.

"Get the fuck back," the Border Patrol agent barks, pushing forward, flicking his wrist so that his billy club extends aggressively at Garcia, exposing the brute violence that underpins the border.

"We don't consent," Garcia tries one more time. "Get. The. Fuck. Back." The agent raises the club and pushes forward at Garcia as though he is about to strike. Garcia keeps walking backward. Sebastian is walking backward. Amelia is walking backward. The children, too, are bracing themselves to be assaulted by the grown armed men.

"Sit down," the agent barks.

The children immediately sit on the burning asphalt. Garcia doesn't sit. He is trying to articulate, now by his actions, that he doesn't consent. The pause is enough to irritate the agent again. "Sit the fuck down," the agent says to the U.S. citizen, again raising his billy club. Garcia finally complies. The border between these two sets of U.S. citizens is as powerful as the actual international border, and the threat of violence can emerge as suddenly and fiercely as an oncoming storm.